Originally Posted by Phred
Wondering if the downside to the "no track bar" is more significant for off road or on the highway ...?
If you correct marginal/poor steering geometry, I say you don't need one.
I've studied the underside of my van, how track bars work, what causes bump steer and why did Ford use a track bar on their leak sprung front suspension trucks. I've concluded that a leaf spring sprung suspension using a track bar is in a bind, as the suspension cycles, working against itself. It also reduces bumpsteer, when the steering tie rod geometry isn't optimal.
Ford did a pretty good job on the leaf sprung trucks, track bars reduce bumpsteer by forcing the tie rod and axle housing to move in a common arc, which is KEY, and a good thing. In order to do that, the track bar forces the entire axle housing to translate (move sideways) maybe 3/4" as the suspension cycles, instead of steer the truck when you don't want it to. The driver never notices this side translation, doesn't feel bumpsteer, has a good experience so Ford sold trucks. Add a lift kit and this all goes to hell in a handbasket.
In my opinion, Ford and customers would have been better off engineering in a 'high steer' type set up, and eliminating the track bar altogether on it's leaf sprung trucks. Instead, in the next generation, Ford got rid of the leaf springs, used coils and a forward facing 4-link, w/track bar. In that later configuration, the housing still translates sideways as suspension cycles, but the 4-link and coils design doesn't resist sideways translation and bind like a pair of leaf springs do. In fact, you MUST locate the housing with a track bar, (or some such device) to prevent uncontrolled sideways translation.
Leaf springs on solid axles don't like to be shoved sideways, so they resist, putting the springs in somewhat of a bind, increasing harshness of ride, and putting undo forces on the track bar and it's mounting brackets. As the leaves cycle up and down, the track bar translates the housing sideways, in doing so, the track bar forces the shackle and spring eye bushing to compress, flex the leaves sideway, they move but under protest, and add apparent stiffness to the front suspension. All bad things.
So far as a track bar being necessary for locating a leaf spring suspension, it's not. My evidence is the fact that manufacturers don't use a track bar of the rear of a leaf sprung rear suspension. I would submit that Ford used track bar to correct poor steering geometry, and minimize bumpsteer.
Because of a trackbar working against a pair of leaf springs, and binding, most of the aftermarket 4x4 van conversions, track bars and their mounts often crack.
In my view, and from my first hand experience, I'd say you want EITHER a track bar, or a high steer set up (where the tie rod from pitman arm to knuckle, is as horizontal as you can get it).